In a system, such as a multiprocessor system in which an open source OS like a UNIX (registered trademark), Linux or the like is operated and a plurality of CPUs, after one CPU in a pair of CPUs as a operative one and a redundant one temporarily fails and is degenerated and switched to the other CPU by performing redundancy operation (synchronous operation), in order to reset the CPUs to a redundant configuration, it is necessary to stop the system once, then perform resynchronization of the redundant CPUs and restart of the OS. The CPUs performing the synchronous operation mean CPUs that execute the same processing simultaneously.
As a specific technique concerning a multiprocessor system including plural processors, Patent Document 1 described below describes a multiplex system that sets one of three or more processors in a normal mode and the remaining processors in a monitor mode to monitor an execution state of the processors in the normal mode, judges the processors in the normal mode as being abnormal when every processors in the monitor mode generates abnormal signals and judges the processors in the monitor mode as being abnormal when one of the processors in the monitor mode generates an abnormal signal.
Patent Document 2 described below describes a redundant system realizes resynchronization of state devices respectively provided in redundant first CPU and second CPU, and when any abnormality occurs in one specific state device among the state devices in the second CPU, for example, and synchronization is necessary, a resynchronization server issues a resynchronization command to the specific state device and a state device corresponding to the specific state device in the first CPU to restart both the state devices.    Patent Document 1: Japanese Laid-open Patent Publication No. 6-30069    Patent Document 2: National Publication of International Patent Application No. 2002-538521
As explained above, conventionally, after performing degeneration of any one of the redundant CPUs that perform synchronous operation, in order to set the CPUs into the redundant configuration again, it is necessary to stop the system once, perform resynchronization of the redundant CPUs and restart of the OS. However, in a backbone system required to perform continuous operation, such a temporary stop of the system causes a problem that the continuous operation cannot be performed.
In the conventional technique described in Patent Document 1, it is necessary to use a dedicated processor having an interface for receiving a control signal from a control unit that detect abnormality of the processor to stop an operation of a processor. In the conventional technique, even when a temporary failure in the processor due to a software error or the like occurs, the processor is disconnected from the system. Since the conventional technique is for determining an abnormal processor on the basis of decision by majority, when abnormality is detected in two processors remaining after detecting, both the processors are stopped.
The conventional technique described in Patent Document 2 is a resynchronization technique for state devices in a particular system; in which restarting all the state devices relating to a state device being abnormal does not affect the states of the other state devices. Consequently, the resynchronization processing for such state devices in the conventional technique depends on functions of an OS that runs on the system and does not apply for a device that run a general-purpose OS without such functions.